Assalamualaikum Can i send text messages to a friend who has sinful app on her phone ? Am i get sin if i send txt messages to her ?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is no harm on you in sending a message to or contacting a person who has forbidden applications on her mobile phone.

It is not forbidden to deal with this person just because she is disobedient with her mobile phone. Contacting her is permissible and sending messages that do not involve helping her in her sin is permissible.

Allah Knows best.